In many applications in which tubes, pipes or conduits are arranged to enable a fluid to flow from one point to another, there is a concern about the occurrence of leaks at some joint or other unattended point. While such a leak in a water pipe may be of little concern, fuel leaks or leaks of some other fluid may result in a potentially dangerous situation or area contamination. In the latter class of applications, it may be desirable to provide some type of coaxial sleeve or shroud intended to contain any leaking fluid. However, known prior arrangements for this purpose have generally been subject to disadvantages such as large size, high cost, difficult in situ assembly, limited adaptability and low reliability.
For example, in passenger aircraft applications potential leaks in fuel lines linking fuel storage tanks to the engines represent a significant safety problem. In view of this, safety regulations require provision of some form of secondary barrier for leak containment, particularly at fuel line joints and fuel line runs in passenger and fire hazard areas of the aircraft. In the past, such secondary barriers have taken the form of metal or rubber shrouds significantly larger than the fuel line, which are assembled around the fuel line at the time of its installation in the aircraft.
Where rigid metal fuel lines are used with assembled joint components to accommodate changes in fuel line direction, the shroud diameter must be significantly larger than the fuel line and joint components. This is necessary in order to enable assembly of the joint and assembly of a rigid shroud or positioning of a flexible shroud over the line and joint in the aircraft. Where flexible fuel lines are used, large diameter shrouds are typically required to enable assembly over fuel line bends of relatively large bend radius. In some applications, shroud sections are installed so as to cover only a joint section of the fuel line. While this may make in-aircraft fuel line and shroud assembly somewhat easier, seal assemblies are then required at each end of the shroud assembly. An attribute of many of these fuel line enclosure approaches is the difficulty of adequately supporting the fuel line within the shroud assembly and of providing adequate electrical grounding between the fuel line and the shroud, where required. As a result, the fuel line may be able to move laterally or experience significant vibration in the environment of an operational aircraft.
Other fluid flow applications may represent less dangerous conditions, but may involve the problem of area contamination. Thus, for example, in a clean room application for electronic assembly, chemical, biological or other use, a leak in a supply tube or pipe may represent a very disruptive risk, so that a practical, reliable and economical arrangement for leak containment is highly desirable. In these and other applications a secondary objective may be to enable actual monitoring and recovery of any fluid which does leak from the supply tube or pipe. This permits both identification of the presence of such a leak and avoidance of a buildup of fluid which has leaked under supply conditions typically involving some degree of pressurization.
Coaxial piping systems have been proposed in order to address some of the considerations discussed above. Rigid pipe systems can be provided using welds or connector assemblies at joints and corners, with some form of spacer inserted to preserve spacing between inner and outer pipe sections. Also, various forms of spacing protrudances can be provided on one or the other hose of a coaxial system utilizing two flexible rubber hoses. At the same time, even though a tubing system using coaxial metal tubes of bendable aluminum, for example, would provide significant advantages of light weight, reliability, long life and small size, so far as is known no practical such system has been available for applications of this type. A basic reason for such unavailability has been the very real problem of how to bend two metal tubes arranged coaxially, without the collapse or severe deformation of one tube or the other. It is also generally desirable to avoid having the inner tube forced against the outer tube during bending. Spacers can be inserted between the tubes, but have generally been unsatisfactory for maintaining structural integrity of the tube during the bending process. While equipment and methods have been available for maintaining structural integrity of a single tube while enabling it to be bent, such approaches have not been relevant to the problem of simultaneously maintaining structural integrity of the inner and outer tubes during the bending of two coaxial tubes.
It is therefore an object of this invention to provide coaxial tubing systems, including a bending sleeve inserted between inner and outer tubes which enables the inner and outer tubes to be bent simultaneously while maintaining structural integrity of both tubes.
An additional object is to provide bending sleeves, for coaxial tubing systems, which are effective to transmit bending forces to and from inner and outer tubes so as to limit tube collapse and deformation, and to maintain annular spacing between the tubes. A further object is to provide such bending sleeves which also encompass one or more longitudinal fluid passageways between the inner and outer tubes.
Other objects are to provide methods for bending a coaxial tubing system while avoiding tubing collapse and to provide new and improved coaxial tubing systems, bending sleeves and bending methods which avoid one or more of the shortcomings or disadvantages of prior coaxial systems and bending methods.